1. Field of the Invention
The method of this invention relates to hydraulic fracturing of subterranean formations by a fracturing fluid. Particularly, this invention relates to control of hydraulic fracturing treatments of tight gas sands.
2. Setting of the Invention
Oil and gas accumulations usually occur in porous and permeable underground rock formations. In order to produce the oil and gas contained in a formation, a well is drilled into the formation. The oil and gas may be contained in the porosity or pore spaces of the formation hydraulically connected by means of permeability or interconnecting channels between the pore spaces. After the well is drilled into the formation, oil and gas are displaced to the wellbore by means of fluid expansion, natural or artificial fluid displacement, gravity drainage, capillary expulsion, etc. These various processes may work together or independently to remove the hydrocarbons in the wellbore to existing flow channels. In many instances, however, production of the well may be impaired by drilling fluids that enter into and plug the flow channels, by insufficient natural channels leading to the particular borehole, of by insufficient permeability surrounding the borehole which may result in a noncommercial well. The problem then becomes one of treating the formation in a manner which will increase the ability of the formation rock to conduct fluid to the wellbore.
Various methods of hydraulically fracturing a formation to increase the conductivity of the formation have been developed. Hydraulic fracturing may be defined as the process in which fluid pressure is applied to exposed formation rock until total failure or fracturing occurs. After failure of the formation rock, a sustained application of fluid pressure extends the crevice or fracture outward from the point of failure. The fracture, propped by a proppant, creates high capacity flow channel and exposes new surface area along the fracture. However, the height of such a fracture should be confined to the zone of interest. No methods are presently available to limit this height.
3. Relevant Publications
A U.S. Pat. No. 3,933,205, Othar Meade Kiel, issued Jan. 20, 1976 and entitled "Hydraulic Fracturing Processing Using Reverse Flow" discloses a method of multiple hydraulic fracturing cycles. The disadvantage to the method of Kiel is that a predetermined amount of the fracture fluid is broken up into multiple treatments to obtain and initiate secondary fractures transverse to the principle fracture. In the method of this invention, it is desirable to create deeply penetrating fractures which are confined to the producing horizon. In order that this may be accomplished, the initiation of secondary fractures or fractures extending into horizons above or below the producing horizon must be minimized.